It is known that, especially nowadays, it is necessary for foams, especially for use in the aircraft industry, for example in seating, to pass highly stringent fire performance tests such as those of the U.S. Federal Aviation Authority, namely FAR Part 25, Appendix F. In particular, the seat cushion and seat back upholstery assemblies all need to meet the flammability requirements of the oil burner test FAR 25 Appendix F, Part II. In addition, each individual component of the seat cushion and back assemblies, e.g. foams, fabrics, interliners and fastenings, must meet the flammability requirements of FAR 25 Appendix F, Part I, a vertical strip ignition test, also required by the UK Civil Aviation Authority, namely CAA8 Issue 2.
Until recently, core foams and dress cover materials were available which would individually meet the small scale ignition requirements of FAR 25 Appendix F, Part I, but in combination could not meet the more severe oil burner test FAR 25 Appendix F, Part II, without the use of a fire barrier material which completely encapsulates the foam core. This could be adhered to the foam or used as a loose liner inside the dress cover, or be integrated into the dress cover.
The normal practice throughout the world is for an inflatable life jacket to be stored underneath the passenger seat, for use in emergency should the aircraft be forced to land on water. There are, however, exceptions to this--notably in the USA and Canada, where the regulations allow for the use of an inflatable life jacket and/or the need for the seat cushion to be sufficiently buoyant to support the passenger in water. Since aircraft seat cushions are predominantly made from flexible polyurethane foams which are open celled, and hence absorb water, this is currently achieved by incorporating a closed cell foam, e.g. polyethylene, into the seat construction. The seat cushion is held in place by the use of velcro type fastenings and this can be readily removed from the seat frame when required, as a buoyancy aid.
However, to date, although the component providing the buoyancy may meet the requirements of the abovementioned FAR 25 Appendix F, Part I (vertical strip ignition) test, it does not meet the abovementioned FAR 25 Appendix F, Part II (oil burner) test for resistance to flammability when in a seat construction, unless it is protected by a fire blocking (usually fabric) material.
Relatively recently, flexible polyurethane foams have been introduced which have been provided with a fire resistance sufficiently high to meet the above oil burner test. This has been achieved by post-treatment of the foam or incorporation into it of a solid flame retardant such as expandable graphite, so that the need for a fire barrier layer was negated. However, for cushions containing a buoyancy foam it was still necessary to block separately, with a fire barrier layer, the buoyancy foam; otherwise the above oil burner test could still not be satisfied.
Expandable graphite referred to above, is a fire retardant known to be capable of imparting high fire retardancy to various materials when incorporated into them. It is a form of graphite containing at least one exfoliating agent such that at high temperatures, considerable expansion will occur.
U.S. Pat. No. 3,574,644 discloses the incorporation into many materials of expandable graphite for conferring upon them flame retardancy. Examples are greases, petroleum oils, asphalts, rubbers, wood, film forming agents such as latexes, paints etc, and synthetic and natural polymeric material such as cellulosics, polystyrene, polyethylene, polyurethane etc. The only foam material mentioned is a rigid polyurethane foam. However, such foams are not flexible and the closed cells of such a foam are easily fractured upon compression, thus rendering the material non-buoyant. For this reason, such foams are of no practical value for providing buoyancy in seating applications, where such compressive forces will of course be experienced.
GB-A-2168706 discloses the incorporation into flexible polyurethane foams of expandable graphite, while U.S. Pat. No. 5,169,876 reports an improvement in such a foam by ensuring that the flakes of the expandable graphite have a size in the order of magnitude of resultant foam cell walls. However, such flexible foams are of an open cell structure and cannot serve as a buoyancy aid.
On the other hand, in the packaging industry and as buoyancy aids, polyolefinic foams have found use. However, in order not to disturb the closed cell nature of the foams, such foams have been rendered fire retardant by the use of compounds providing halogen and/or phosphorous, or by modifying their structure so as to provide the presence of such compounds or by using small particle size compounds such as antimony oxide, borax or melamine containing compounds.